78 PATAGONIAN EXPEDITIONS : PAL/EONTOLOGY. 



Rio Chico, 5 single valves; Shell Gap, upper horizon, i sp.; High Bluffs, 

 S. W. of Lake Pueyrredon, 8 sp.; Lake Pueyrredon, base of Tertiary, 25 

 sp.; Lake Pueyrredon, 600' above base, 26 sp. 



Distribution: San Josef and San Julian (Sow.); Gulf of San Jorge 

 (specimens sent by v. Ihering to the U. S. Nat. Mus.); Santa Cruz (speci- 

 mens sent by v. Ihering to the Princeton Mus.); of Lahille's localities: 

 S. Jose, Pyramides, Madryn, only the first is supported by other authors. 

 In New Zealand, this species is recorded by Hutton from the Oamaru and 

 Pareora beds (Oligocene and Miocene). 



20. TEREBRATELLA GIGANTEA spec. nov. 



PI. XIV, Fig. 2"-'. 

 1897 Magellania venosa Pilsbry, in: P. Ac. Philad., p. 330. 



Shell oval or elliptical, on the average a little broader than in the pre- 

 ceding species ; dorsal (small) valve slightly convex, ventral valve strongly 

 convex ; beak incurved, with a large foramen ; beak ridges blunt. Sinus 

 indicated only by a flattening of the dorsal valve and a slight curve of 

 the margin, but in many cases not at all visible. Surface smooth. Hinge 

 and septum considerably thickened in old age. 



Measurements: Length, 67, 66, 64, 61, 59, 52, 48, 45, 37, 26, 14 mm. 

 Width, 54, 51, 56, 50, 54, 41, 45, 43, 38, 24, 13 mm. 



An isolated smaller valve is 58 mm broad, which would indicate an 

 individual measuring over 70 mm in length. 



Remarks: This is the largest species of the genus hitherto known. The 

 generic position is beyond doubt, since I have succeeded in isolating the 

 brachial apparatus, which is represented in fig. 2 d on plate XIV. 



The external shape is somewhat variable: younger individuals are 

 broader in comparison with older ones, but I have only one case in which 

 the width exceeds the length of the whole shell (see above). This broad 

 shape passes gradually with age into a more elongated one, as the lines 

 of growth indicate. The more elongated form is attained at different 

 ages (see measurements above), so that sometimes larger individuals still 

 retain the broad outline. Both valves are convex, but the smaller one 

 distinctly less so. In old individuals the median septum, hinge plate and 

 hinge processes are extremely thickened and swollen (figs. 2 e ' f , pi. XIV.). 



Record of specimens : Cape Fairweather; 26 complete specimens and a 

 large number of isolated or broken valves. 



